tv [untitled] October 13, 2010 12:00am-12:30am PST
does that mean if that occurs how will we adapt our urban areas to adeal with this? at the present time we have something in excess of 80,000 properties at immediate risk from flooding within urban areas in the uk. the annual damage cost at the moment is something like $270 million pounds. that's about $500 million per annum, and the annual cost of flood mitigation is on the order of $320 million pounds. that's a huge sum of money that's already invested in flood protection work in the uk. when we look at the impact of climate change and particularly the effects on the sort of storm events that leads to flooding in urban areas and, indeed, in rural areas as well, we are looking in the uk at something up to around 40
percent increase in rainfall intensity. and when we model that effect on our urban drainage systems on our river channels, we see that that will lead to something understandablely of the order of 40 percent increase in the flows in those drainage systems. but because those drainage systems are already nearing capacity, that has a disproportionate effect on the amount of flooding and the amount of damage that might occur. we expect to see 100 percent increase in flood volumes on the surface, doubling the flood volume. 130 percent increase in the number of properties affected and a 200 percent increase in the damage of that flooding. that's a three-fold increase in damage costs. that's just looking at that fairly narrow band of flood control and damaged property in urban areas. one of the difficulties of trying to look at the future is
the uncertainty of what the future might look like. this graph is taken from the government's foresight project on flooding and coastal defense and the effects of climate change. there are four bands on here. the left-hand band is the present scenario. that's a summary of the average annual damage as a result of flooding in the uk. then we have four other bands and these are the four future scenarios. this is looking at really the world economic environment and how that might change in the future. the left is an economic environment that is based on world markets driving the economy. the next one is based on natural enterprise driving the economy. the next one is one of local ownership, everything reduced to regional economy and the right is everything driven basically on the basis of environment protection. our feeling at the moment is that it's the second of those that is the most likely, that
is the national enterprise model. and we can see as we look at that that there's going to be very substantial increase in flooding in the future and within that, that the biggest increase is likeliest to occur within our urban environments. so although we will see a very significant increase in flooding due to river flooding and flooding due to coastal impacts, the biggest cause or biggest increase in flooding in the future is likely to be within the urban area. what we've been wrestling with is how might restart to adapt to that? how might we cope with that future? this one shows the number of properties affected. what's interesting about this one is there isn't the same differential between the future assumptions that irrespective of how we see global economy developing we're likely to see something in the order of 4 to 5 times the number of properties affected by urban flooding in the future if we continue with our current
levels of investment. we have exactly the same picture if we look at coastal impacts as well, that shows the same sort of picture, although the increase is perhaps more dramatic. we see here something like an 8 to 10 fold rise in the number of properties affected. so how might we deal with some of this? one of the things the projects have been looking at is what would be the implication of continuing with our current policy of managing urban drainage, managing river flooding, and managing coastal defense? what we can see is that the storage solutions we're dealing with problems in urban areas, the cost of those would be likely to increase something between two and four times present day values. if we move to a policy of
storage retention to increase conveyance, we can contain that cost a little bit. the cost rises are not so high there, two to 2.3 times present day values, but that does not account for the impact on the urban communities, the disruption and loss of businesses that would be caused by that reconstruction of our urban systems. if we were to control the discharges to present day impact standards, then we will be looking at something like 3 to 10 times the cost of managing the discharges and overflows. and as has already been said today, given that our investment in infrastructure is competing in urban areas with other investments for education, police and so on, it's very unlikely that all of that money is going to be available to deal with urban protection against climate change from flooding. so the conclusion there is it
is unlikely that any of the conventional strategies in themselves are going to be feasible in the future long-term because of the impact of climate change. i'd like to give some examples of some slightly alternative solutions that are being proposed now and how those might change and some of the headline solutions. the first message is that when we're looking to control river flooding and urban flooding, then conveyance is likely to become more popular than storage and attenuation schemes. and this shows a length of completely new river that's been built to the west of london. this is the jubilee river. it is basically a duplication of the river thames. we are likely to see more conveyance solutions of this type being constructed in the future. many of you will be familiar
with the thames garage project. this has been in operation for quite a number of years and essentially protects the whole of the essential london area from rising sea levels. this will have to be replaced with a much bigger barrier in the future and starts have already been made on planning and estimating costs. it will be totally impossible to defend all coastal areas from sea level rise in the future. it is only the high value areas where we will be able to afford such protection from coastal changes. in our urban areas as well, as i said, we will not be able to afford simply to increase the size of our infrastructure to deal with the increased storm events we will see as a result of climate change. this is a picture of severe
flooding in glasgo, scotland in 2002. you can see the contribution that the drainage system is making here. you can see the water streaming out of the drainage system on to the surface. the flood event showed the urban system was full to capacity approximately 20 minutes into the storm. it only conveyed something like 20 percent of the flood water. the storm lasted for about 4 hours. 80 percent of the flood flow was conveyed on the surface. this is a good example, this is a hundred year event. this is a good example of the sorts of extreme events that we're going to see much more frequently in our urban areas. our urban drainage systems already are incapable of conveying most of the flood water that arises from intense
storms and they are likely to be even less likely able to carry that in the future. so how are we going to cope with that aspect? what we're starting it look at in the uk is how do we design our urban areas better so these flood flows can be managed above ground, recognizing that major above ground system is going to have to play a key role in conveying storm water in the future. by converting flood pathways, by increasing space between buildings and even designating sacrificial areas that can be sacrificed in a flood event. the last part i want to say is talking about a new project
that is being piloted in the uk in an urban environment which applies just the same to rivers and to coastal defense. i'd like to perhaps explain a little bit about why integrated approach is important. this is a picture of a relative small area of flooding in the north of england. small picture but i'd like to take you through. the first in the top left shows the source of the flooding. this is in windsor and it developed because a large area of largely rural of land got completely water logged and then during a storm event that water washed off that area into the urban area. the responsibility for managing that drainage lies with the local drainage authority, which is the drainage board. it flowed on to highways in the area -- you see in the top
right picture highway flooding. responsibility for draining the highway is the local highway authority. it then flowed into the properties on the left of the picture. as soon as it crossed past the wall there into the property, the responsibility for that drainage shifted to the drainage -- the responsibility of the local water company, which is a private company responsible in part for draining property. it went in through the front doors of those properties, it went down one floor and came out through the back doors, as we can see in the bottom left-hand picture, and drained off. and underneath, as we see in the bottom right, behind some of the properties is also an underground culvert which also burst open causing flooding. that is the responsibility of the local -- a different local drainage authority. there's four different agencies involved with managing this very simple and localized flooding event. you will see on the top right the people looking rather
despondently over the wall. they don't care who is responsible; they just want the problem fixed. different jurisdictions have to start developing integrated approaches or we will not be able to serve the public properly and we will not be able to adequately cope with climate change effects. second reason why integrated approaches are important is that in almost all cases urban flooding is very, very complex. it might be due, as the top left picture shows, to overloading of the drainage infrastructure within the urban area. as the top right-hand picture shows, it might be due to coastal inundaition, or it might be due to river flooding.
most likely is that it will be due to all 3 concurrently. how we address that from an engineering perspective is very difficult. despite all our advance modeling tools, we still have some way to go firstly to properly explain all those interactions and secondly to be able to develop a proper engineering integrated solution to those problems. and then, thirdly, one of the problems we have with flood protection is that drainage engineers and flood protection engineers, for many, many years in the developed world have been working in their own compartment. as the picture shows, this is always the way we did our urban drainage planning. but what we're beginning it realize is that we have to think about this in the much wider context of urban areas and recognize that there are other agencies involved, not just the drainage agencies.
there's a transportation agency, the planning agencies, health and social services and so on. when we start to get these agencies around the table all working together for common objectives, we have a much better chance of coping with some of the challenges that we have to face. and, finally, what this graph shows, again, these 4 future scenarios on the right, we've seen the orange ones before, the potential effects of conventional solutions, current scenario on the left-hand side, very graphic representation of what we may sense, but in yellow we see the current potential of integrated approaches. if we get all the stake holders together and we get an integrated understanding of the
technicalities of the problem, then we have a chance of developing solutions that will cope with future climate change in a way that may just about be affordable. so overall i'd like to conclude with just a few key messages. firstly, that conventional approaches for flood protection are probably going to be unsustainable in the long-term likelihood of climate change. secondly, extreme events do need to be managed. we need to think about how do we manage flood water on the ground. thirdly, that conveyance is likely to be more cost effective than the more traditional attenuation and storage solutions in the future. coastal protection is only likely to be affordable to protect high value areas. urban flooding must be managed above ground as well as below ground and that integrated approaches are the way forward.
thank you very much. . >> good morning, everyone. my name is tom franza, i am the assistant general manager for the waste water enterprise of san francisco public utilities commission. and i really appreciate the opportunity today to speak to you about a very specific problem we face in san francisco with rising sea level. the previous speakers i think have done an excellent job giving an overview of what we might expect to happen with climate change and i wanted to bring up a very specific
problem and how we might approach that, hopefully to let all of you see what we're doing and perhaps generate a lot of discussion later with people who have similar problems and what we might all do to resolve this. so here we are, san francisco, surrounded by lots of water. and i want to show you a bit about how san francisco's waste water system works and then how rising sea level will impact that. we have a combined sewer system. san francisco's system started to be built in the 1860's, so it's pretty well been built out by the 1930's or 40's. it was built as a combined sewer system and what that means is that the sanitary sewage flow and run off from streets and storm drainage all flows in the same pipes.
the system is built now with a large storage and transport system, the idea being we collect on a rainy day we can collect a lot of the storm water, store it in the system, and then treat it later when the rain stops. this little diagram shows you how the system would work. on a dry day, most of the sewage would be coming down the pipe, it would be flowing into the big transport structures that exist around the city, probably flowing right at the bottom of these very large structures. they are on the order of dozens of feet wide and dozens and dozens of feet deep and they have little sloped bottoms and q nets at the bottom where most of the dry weather sewage flows all the time. that waste water is transported to the treatment plant. on a rainy day, those transport
storage structures, the large structure represented in the center of the picture, start to fill and they fill dramatically. it always amazes me to watch a flow gauge or a level gauge on one of these structures. just to give you an idea of their size, if any of you are familiar with the great highway out by ocean beach, there's one of these structures that runs under the great highway that's about two miles long, about 40 feet wide and about 40 or 50 feet deep and it can hold 50 million gallons of runoff. i can watch the level gauge on our monitoring stations just creep up when the rains start to get hard. so the amount of water that we handle in a storm is absolutely tremendous. well, what will happen is we have plants and pumps that can pump this large volume of water it a large degree to our treatment plants where we can give it in many cases full secondary treatment. but on very peak storm days,
and this is something that the other speakers have brought up and how these intense storms are problematic for us, when we get a big storm we are pumping and treating all we can but we don't have enough capacity to handle all the water. so what will happen is these structures will fill and then they will discharge. we call that a combined sewer discharge into the bay or into the ocean. i want you to take note of that pipe that's represented going out to the right there where we drain into the ocean. there's where we start to get into our problem with rising sea level. this is a little bit bigger representation of the slide will showed that was showing the bay side of the city. this is sort of our transport storage structure around the entire city. we call it a moat. it's the way we collect rain water for later treatment. as i said, in light to moderate storms we can do a pretty good job of collecting all of the
rain water and sanitary sewage and running it through the treatment plant. in fact, there are probably, in terms of calendar days, there might be 14 to 15 calendar days a year where we would actually have a combined sewer discharge. those would be in the heaviest storms. around this moat structure in the city there are 36 outfalls. these would be the overflow points when the system fills to capacity and we can't treat any more. the west side of the city doesn't present an immediate problem for us yet because of its elevation. it's a bit higher than we think will be impacted in the next, say, 30 to 50 years by rising sea level. it's the bay side of the city where we anticipate some problems. this is a photo, it's a little bit difficult to see, but stormy days are kind of gray and dreary and it's tough to get a bright picture of this. what you are seeing here is one
of our combined sewer discharge structures and what you are seeing is the discharge of combined sewage on a very heavy rain day, probably 90 to 95 percent rain water, blended with domestic sewage of about 5 percent. i want you to note where you see the sewage coming out of this structure and when we go to the next slide, i want to compare that with the sea level. the trend you see here you have seen before. it's data that clearly shows a historical trend of rising sea level. there's just no doubt about that. and on the left-hand side of the picture i wanted to represent at the far left the transport storage structure, the bay would be on the right side of the dark blue bar and
the dark blue line, the gap represents the weir. that's where the overflow point would be. if we progress on with our projections of where sea level is going, the horizontal red bar represents the lowest elevation of our current weir structures. if we look at ipcc projections, for example, of where tides are going, it doesn't take too long -- not too many years, maybe about 2013, 2014, we get to a point where at peak tides we have very regular occurrences of bay water actually topping the weir and coming back into our system. the bad news is we actually see this happening now. the photo on the left is that
same structure you saw discharging in a previous slide. the weir structures are the slots underneath. the lower right photo you are seeing a high tide that is actually not happening on a stormy day, not when we're having a lot of wind and tidal surge; it's just a very high tide that's actually topping over the weir and coming back into our system. the problem that we face i think is represented very well here in that if this becomes -- right now this is maybe a several times, several days a year event. probably it occurs for several hours and then stops. so we can sort of deal with that. the issue is, though, if this starts to become a daily occurrence, which it could well be with a sea level rise of a foot or a foot and a half -- not that much -- then we have big problems.
i noticed a lot of my waste water colleagues in the audience and i think we all understand what the problem is. it's really, simply stated, it's two things. our treatment facilities aren't designed to handle salt water. we have biological treatment systems that operate in a fresh water mode. salt water intrusion -- actually we've had this happen to us in san francisco where we have had a breach of our system, about 15 years ago, i think, and we had a huge influx of salt water into the system. the chloride levels got very high and that produced great stress on the biological treatment systems to the point that we were worried that we were going to lose the entire treatment system for a period of time. once you lose a biological system like that, it takes some time to regenerate.
luckily we avoided that problem. one issue is that with a lot of salt water entering the system, our current state of treatment processes just won't work very well, if at all. the second problem we have is basically your sewage system is full of bay water so if you do have a storm or a rain event coming, then you get back to the surface drainage problem that david talked about, the surface drainage won't have anywhere to go. obviously big problems with that. clearly if we would allow that to happen, we could easily experience huge flooding problems, back-ups in the areas of the city that are susceptible to this sort of intrusion. on the next slide, i want to talk a little bit about the way the system is designed.
you have to -- you're going to have to allow for overflows because you are not going to be able to treat everything that comes at you. your weir levels have to be -- in the past, these things were designed a long time ago and assume -- there's an assumed sea level, so you would set your weirs at a point higher than that so any sort of high tide you wouldn't expect to have any sort of inflow into the system. but the weirs have to be set low enough that if you have a large inundaition, the drainage will happen in a manner that won't cause a back-up in the system and flood properties and streets like you saw in the previous slide. we have ways of prevents the back flow and that's what we really have to look at in the next little while. in fact, we have a 30-year master plan we're working on now that's looking at this
problem of inflow into the system from high tides in a very serious way. we believe we probably have to start implementing some back flow prevention measures, i'd say, within the next several years, probably 3 to 5 years. it's already happening now and it's just going to get worse. so some of the things we could probably do would be, for example, these -- we call them duck bill valves that we could install on some of our weirs. sounds simple enough, but if you remember the configuration of the weir i just showed you, they are quite long and we don't have too many sort of pipes, small pipes, like that that just end and you can put a duck bill on the end to prevent the flow from coming in. but conceptually you can do this with a long weir.
here's another example of a long weir structure. this is sort of south of monster park along the bay. on the lower left you can see sort of the weir arrangement as it currently exists. one of our concepts would be -- it's a little hard to see, but you can sort of wall off those existing weirs and put some sort of a duck bill type of back flow prevention in there. so we see this as a near term solution to a current problem we have, something we can start doing right away, and i think my engineers suggest that this would probably protect us i'd say for the next 30 to 50 years. if this is all we did, we could probably avoid serious problems with salt water intrusion. start looking at the longer term, i don't really know what you